1. Field of the Invention
The present invention relates to a molded-case circuit breaker with a main contact interlock feature, and more particularly, to a molded-case circuit breaker with a main contact interlock feature which prevents improper operation of a tripping mechanism that trips main contacts when the main contacts fuse together.
2. Description of the Conventional Art
In general, a molded-case circuit breaker (MCCB) is an electrical device that protects a circuit and a load by automatically interrupting the circuit when there is an electrical overload or short circuit. The circuit breaker typically includes a terminal portion provided on the front and rear and forming a circuit connection, a mechanism divided into a stationary contact and a movable contact and mechanically opening and closing a circuit, a trip portion detecting an over-current or short-circuit current in the circuit and causing the mechanism to trip, and an extinguisher for extinguishing an arc produced when interrupting a fault current.
In the circuit breaker, the mechanism requires a function for verifying main contact positions, in addition to its basic functions such as allowing and breaking current. Verification of main contact positions is for the purpose of allowing the user to recognize circuit conditions and preventing safety incidents by holding the handle of the mechanism in the input position to prevent it from moving to the off position when a movable contact and a fixed contact fuse together while current is applied (conducting state). This function of the circuit breaker which prevents the handle from moving to the off position is also called an “isolation feature”.
The main contact position verification function may be implemented by blocking or tripping. In the blocking method, the handle is not moved to the off (interrupted) state even if the user exerts force to the handle to move it to the off position. On the other hand, in the tripping method, when the user operates the handle to move it to the off position, the mechanism is tripped so that the handle is held in the on state (or tripped state).
Now, a description will be given of a molded-case circuit breaker that can maintain the main contact position verification function, reduce the number of parts, and improve improper operation of the tripping mechanism by using the tripping method.
FIGS. 1 to 3 depict a switch mechanism of a molded-case circuit breaker according to the conventional art. The figures show the off state, on state, and fused state, respectively.
The switch mechanism 1 includes a switch lever 4 that is rotatably mounted on a lever shaft 17 mounted on a part of a side plate 2 and moves to the on, off, and tripped positions, a handle 3 that is attached to the switch lever 4 and applies manual operational force to it, an upper link 6 rotatably mounted on a latch 19a, a lower link 7 rotatably mounted on a first shaft pin 15a of a shaft 14, a link shaft 18 to which the upper link 6 and the lower link 7 are attached, and a main spring 5 that is attached to the link shaft 18 and provides elasticity.
When the user turns the handle 3 from the off state (interrupted state) to the on state, the link shaft 18 rotates counterclockwise by the force of the main spring 5 attached to the switch lever 4 and pulls the upper link 6 and the lower link 7 into the shape of a nearly-straight line and rotates the shaft 14. A movable contact 12 of a contact region 11 comes into contact with a fixed contact 13 and creates a conducting state (on state). The link shaft 18 is placed on the left of the lever shaft 17, and the switch lever 4 is locked in the on state. A transition from the on state to the off state occurs in the opposite way.
Meanwhile, a tripping mechanism for implementing the main contact position verification function is mounted on the right side of the mechanism. The tripping mechanism for implementing the main contact position verification function includes a first link 8 connected to a second shaft pin 15b, a second link 9 connected to a first link 8, a trip link 10 that rotates by the force of the second link 9, a nail 16, and a latch holder 19b. The second link 9 has a long hole along which a pin slides.
In the case of a normal interruption, the shaft 14 rotates, so the first link 8 connected to the second shaft pin 15b moves downward, thus keeping the trip link 10 from operating (see FIG. 2 and then FIG. 1). That is, in normal on and off actions, the first link 8 and the second link 9 move within a certain area and do not affect the trip link 10.
When the contacts fuse together as shown in FIG. 3, the shaft 14 does not rotate beyond a predetermined range. Thus, the first link 8 does not move downward but is pushed by a pressure portion 4a of the switch lever 4 and rotates clockwise and pushes the second link 9. Accordingly, the second link 9 rotates the trip link 10, and the trip link 10 rotates the nail 16, thereby releasing the latch holder 19b. The latch holder 19b releases the latch 19a, thereby tripping the switch mechanism 1.
Because the link shaft 18 of the tripped switch mechanism 1 is positioned more to the left than the lever shaft 17, the switch lever 4 is always in the on state (or tripped state). As such, the positions of the main contacts of the circuit breaker can be detected, and a fusion of the contacts can be detected.
However, in the conventional art, the tripping mechanism for verifying main contact positions includes a first link 8, a second link 9, and a trip link 10, and the first link 8 can move relatively freely. Therefore, there is a risk that, when the switch mechanism 1 performs an on operation, the second link 9 might be pushed by the collision of the first link 8 on it and touches the trip link 10, causing the switch mechanism 1 to trip.